Busy Corp Sent a Letter on January 12^th to Slow Co

Busy Corp. sent a letter on January 12^th to Slow Co. offering to sell its main office building for $250,000, stating that its offer was open only until January 20^th, and it must have a response from Slow Co. by then. Slow Co. received the letter on January 14^th and prepared a letter of acceptance on that day but had not posted it. The next morning Busy Corp. called and said that it had changed its mind and was withdrawing its offer.

A) There was a contract as soon as Slow Co. wrote the letter of acceptance and the revocation is too late.
B) Since the revocation was made by telephone and the offer was made by letter, the revocation is not effective.
C) The revocation was effective because it was communicated to Slow Co. before the acceptance was sent.
D) The revocation was effective because it was communicated to Slow Co. before the acceptance was received by Busy Corp.
E) All of the above are false.